Synergistic effect of polyimide charring agent and hexaphenoxycyclotriphosphazene on improving fire safety of polycarbonate: High graphitization to strengthen the char layer

Abstract

To meet the increasingly stringent requirements for the excellent fire safety, low addition, low cost, and good mechanical properties for polycarbonate (PC), a novel aromatic polyimide (API) charring agent was synthesized and used synergistically with hexaphenoxycyclotriphosphazene (HPCTP) to flame‐retardant (FR) PC. The incorporated API and HPCTP improved FR performance and the fracture toughness of the PC, simultaneously. The 4H‐2A passed the UL94 V‐0 rating with a limited oxygen index of 32.5%. Moreover, the heat release rate of the PC was also suppressed significantly by the dense and strengthening carbon layer. The mechanism of synergistic charring effect of API and HPCTP were analyzed: In the initial and developing stages of combustion (below 450°C), the quenching effect and dilution effect of HPCTP played a major role in flame retardancy; and due to the barrier function of the highly graphitized char layer, the combustion process rapidly enters weakening stages (above 450°C) and finally extinguishes. Moreover, it was founded that API improved the antiimpact performance of PC matrix, which offsets the negative effect of HPCTP on the impact performance of PC matrix.

Preparation and Characterization of Transparent Polycarbonate with High Flame Retardancy and Smoke Suppression

“…Under heat radiation, the HSPP in PC composite was first decomposed to release sulfonates moieties, which behaved as acid sources to catalyze the isomerization and Fries rearrangement of PC and promote the rapid formation of intermediate char at low temperature. With combustion proceeding, the phosphazene moieties began to decompose into phosphorus-containing compounds and free radical (such as PO • and PO 2 • ), which captured oxygen atoms to catalyze the further crosslink of above intermediate char and eventually improved the graphitization degree and integrity quality of residual char layer at high temperature. The high-quality char layers with the intumescent, integral, and compact morphology exerted outstanding barrier and protective effect and finally endowed PC/HSPP composites with excellent flame retardancy performances.…”

“…• ), 24 which captured oxygen atoms to catalyze the further crosslink of above intermediate char and eventually improved the graphitization degree and integrity quality of residual char layer at high temperature. The high-quality char layers with the intumescent, integral, and compact morphology exerted outstanding barrier and protective effect and finally endowed PC/HSPP composites with excellent flame retardancy performances.…”

The Influence of Substituents in Phosphazene Catalyst-Flame Retardant on the Thermochemistry of Benzoxazine Curing

“…The HPP concentration more than 10 phr allows to achieve the V-0 flammability category. The HPP is a well-known commercialized flame retardant which efficiency was proved by many works [ 22 , 36 , 37 ]. HCP affects the flammability of benzoxazine resin at a content of 5 phr and more.…”

Polyacrylonitrile/Phosphazene Composite-Based Heat-Resistant and Flame-Retardant Separators for Safe Lithium-Ion Batteries

“…In this work, we fabricate PAN-based porous composite membranes, incorporating hexaphenoxycyclotriphosphazene (HPCTP) as a flame-retardant agent by electrospinning. HPCTP is a highly thermally stable phosphorus-rich compound, and it is widely used in heat-resistant polymer materials. − The flame retardancy of HPCTP comes from phosphate, metaphosphate, and polyphosphate generated during thermal decomposition, which can form a nonvolatile protective film on the polymer surface to isolate it from the air. Simultaneously, nonflammable gases, such as NH 3 , N 2 , and CO 2 , are released to block the supply of oxygen .…”